(1) Field of the Invention
The present invention relates to a method for treating synthetic pulp particles, and pulp particles composed of a synthetic polymer.
(2) Description of the Related Art
Pulp particles composed of a synthetic polymer such as a polyamide or polyester have attracted attention as a material of an electrically insulating paper, a friction material or a heat-resistant flame-proof article, because of their excellent electrical insulating property, heat resistance, and other properties. It is considered that pulp particles composed of a wholly aromatic polyamide such as poly(metaphenylene isophthalamide) or poly(paraphenylene terephthalamide) have various excellent characteristics and an especially high utility, but, for example, the synthetic pulp particles disclosed in Japanese Examined Patent Publication No. 35-11851 are defective in that when a paper is prepared from these synthetic pulp particles according to the wet method, since the paper-forming property is poor, it is difficult to obtain a paper having a uniform formation, and when the synthetic pulp particles are formed in an electrically insulating article, the insulating property is unsatisfactory.
As means for eliminating these defects, there can be considered a method in which pulp particles are beaten by a beater or the like to the freeness. The relationship between the freeness and the physical properties of the formed paper is illustrated, for example, in "Pulp and Paper", written by Katsumoto Atsugi, and the relationship between the freeness and the insulation breakdown voltage (BDV) is illustrated in "Electrically Insulating Paper", written by Yuichiro Take et al, and it is suggested that a pulp having a high Schopper-Riegler freeness gives a formed paper having good physical properties. It is confirmed that this also holds good with respect to synthetic pulp particles, and in order to obtain good physical properties, synthetic pulp particles having a Schopper-Riegler freeness of at least 30.degree. SR are preferably used. However, the handling property of pulp particles having such a freeness is bad. For example, when pulp particles are prepared by introducing a solution of a synthetic polymer into a coagulation bath, if pulp particles giving a paper having good physical properties are formed, the freeness inhibits the operation of separating the formed pulp particles from the slurry or the operation of washing and purifying the separated pulp particles, resulting in a reduction of the productivity.
As is apparent from the foregoing description, synthetic pulp particles have such contradictory properties that, if it is intended to obtain pulp particles giving a paper having good properties, the handling property is degraded at the steps of forming and treating the pulp particles, and this is a serious problem in the industrial production of good pulp particles.